Thermoplastic resins such as polyester and polyamide, and thermosetting resins such as epoxy each have excellent moldability, mechanical strength, and electrical characteristics for a general-purpose resin and an engineering plastic, and thus have been used in various fields including the fields of electricity and electronics. In addition, resin materials obtained by processing and molding those resins are required to be flame retardant in terms of safety for the purpose of preventing a fire at a high temperature. For example, specifications such as UL94 have been provided as flame retardance grades.
It is generally known that a halogen substance is effective in making such a resin material flame-retardant. Flame retardance is imparted to the resin material by adding a halogen-based flame retardant to the resin. The mechanism of imparting flame retardance to the resin by the halogen-based flame retardant is said to be as follows. That is, a halogenated radical is produced mainly by heat decomposition, and the produced halogenated radical captures an organic radical being a combustion source to stop the chain reaction of combustion, whereby high flame retardance is expressed.
However, a flame retardant containing a large amount of halogen compound may generate dioxin and the like depending on combustion conditions, so there has been a growing demand for reducing the amount of halogen in recent years from the viewpoint of reducing a load to the environment. Therefore, various non-halogen-based flame retardants each containing no halogen-based compound have been examined.
Inorganic flame retardants such as a metal hydrate and red phosphorus, triazine-based flame retardants derived from carbamide, organophosphorus-based flame retardants such as a phosphoric ester, and the like have been examined as such non-halogen-based flame retardants. In the case of a metal hydrate such as aluminum hydroxide or magnesium hydroxide, which does not have a very high flame retardance imparting effect, the metal hydrate must be blended with a large amount of resin. Therefore, the moldability of a resin is apt to deteriorate and the mechanical strength of a molded article to be obtained or the like is apt to reduce, thereby causing a problem that applications of a usable resin processed article or the like are limited. In addition, a molded article of a triazine-based flame retardant is apt to have gloss, so the design of the molded article is limited. The gloss of the molded article can be frosted by being blended with a delustering agent such as talc or calcium carbonate, however, there remains a problem in that toughness and flame retardance of the molded article deteriorate. In addition, red phosphorus is apt to inhibit electrical characteristics owing to insufficient dispersion, generate a dangerous gas, reduce moldability, and cause bleeding, though it has a high flame retardance effect.
For example, Patent Documents 1 and 2 below each disclose that each of red phosphorus and aluminum hydroxide is used in combination with silica gel having an oil absorption of 70 to 250 ml/100 g in order that the flame-retarding effect of each of red phosphorus and aluminum hydroxide may be improved.
On the other hand, for example, Patent Document 3 below discloses that a piperazine salt of an acidic phosphoric ester having a phosphorinane structure or alkylenediamine salt having 1 to 6 carbon atoms is used as a flame retardant being an organophosphorus-based flame retardant such as a phosphoric ester.
In addition, Patent Document 4 below discloses a flame retardant for a resin mainly composed of a salt composed of an aromatic phosphoric ester such as monophenyl phosphate or monotolyl phosphate and an aliphatic amine such as piperazine.
Further, Patent Document 5 below discloses that a phosphorus-containing phenol compound is used as a flame retardant for providing a flame-retardant epoxy resin which exerts an excellent flame retardance effect as a halogen-free flame-retardant prescription and which is excellent in physical properties of a molded article such as heat resistance and water resistance and in adhesiveness in an electrical laminated plate application.
Still further, Patent Document 6 below discloses an organic cyclic phosphorus compound having a bifunctional hydroxyl group particularly useful as a stabilizer for a polymer compound or as a flame retardant.
Patent Document 1: JP 2002-256136 A
Patent Document 2: JP 2003-49036 A
Patent Document 3: JP 2002-20394 A
Patent Document 4: JP 2002-80633 A
Patent Document 5: JP 2002-138096 A
Patent Document 6: JP 5-331179 A